We propose to explore factors and events involved in asbestosis cancer. Inoculation of fibrous glass pledgets containing asbestos fibers into the pleural spaces of mice will be carried ou according to the method of Stanton. The carcinogenic process will be followed and analyzed employing a methodology which we have previously developed for the study of foreign body tumorigenesis. Specifically, the following questions regarding asbestos carcinogenesis will be investigated: Cell type of tumor origin; frequency of preneoplastic foci; morphological and cultural characteristics of preneoplastic cells; their mono- or pluriclonal origination and expansion; preneoplastic kinetics and maturation stages at the tissue and cellular levels; timing and nature of physical interaction between asbestos fibers and cells at various defined stages of the carcinogenic process; the role of tissue fibrosis and phagocytic macrophage activity. In view of the fact that asbestos and other tumorigenic fibers cannot easily be eliminated from the environment of an industrial society, we need a deeper and detailed understanding of the carcinogenic process in asbestosis if we want to approach prevention and cure by different and additional means.